Hammerin' Harry, or Daiku no Gen-san ("Gen the Carpenter"), is a side-scrolling platformer and the first game in Irem's Hammerin' Harry/Daiku no Gen-san series.
Harry/Gen takes on the Rusty Nail Construction Company after it destroys his home as part of their construction work. Harry's main weapon is an enormous mallet that he uses both for offense and defense: he can hold it out in front and above to shield himself from projectiles. Harry/Gen can also find power-ups to give himself more health or temporarily strengthen his hammer.
The game was originally released in the arcade before being ported to the NES and Famicom later the same year. This port was only available in Japan and Europe. The port was forced to remove certain mechanics like bashing boxes into foes as well as one of the game's six stages in order for the game to work on the limited tech of the console, and some of the boss fights were edited too. However, the NES version does retain the original arcade game's memorable voice samples. The NES version also allows Harry/Gen to take up to three hits, rather than the single hit K.O. the arcade version enforces. The original version saw a PC and Mac release with Irem Arcade Hits.